What would happen if you ate nothing but processed diet foods for a month? This has been studied. The results are terrifying.

The Diet That Made America Fat

Back in the 1990's, low-fat diets were all the rage. According to all the dietician clones and fitness "celebs" of the time, all you had to do is eat as little fat as possible and you'd be lean and healthy.

...and America got fatter. Much fatter. And sicker too. Type-II diabetes and pre-diabetes skyrocketed, hormone levels were wrecked, the word "muffin top" entered the vernacular, and junk food manufacturers got even richer. Food makers just stripped out the fat in their salad dressings and granola bars and replaced it with more sugar.

Even though we know better these days, the market is still flooded with foods that have "fat free!" and "low fat!" emblazoned on the labels. And just like the 90's, these foods are usually laden with sugar in one form or another.

So what happens when you eschew dietary fat and eat a lot of sugary "diet" foods? A recent study looked into this. What they found was actually more shocking than they expected.

The Study

Researchers out of the University of Georgia wanted to see what would happen if they fed rats a "popular diet foods" diet. In other words, the rats ate fat-free, high-sugar foods similar to what the average human housewife gobbles down while watching The View.

The subjects were divided into three groups:

A low-fat, high-sugar group

A high-fat, high-sugar group

A balanced diet group

After four weeks of eating like this and having their body composition tested with teeny-tiny little calipers, you can guess what happened: the high-sugar groups got fat. But it gets more interesting.

The Surprising Part

"Our research shows that in rats fed a low-fat, high-sugar diet, the efficiency of generating body fat is more than twice as high," said the study's principal investigator, Krzysztof Czaja.

In fact, the low-fat, high-sugar rodents needed less than half the number of calories to generate the same amount of body fat. Basically, the rats that got fat did so without consuming significantly more calories than the rats fed a balanced diet.

So much for "calories in, calories out" and "a calorie is a calorie." Food quality made the difference here, not total calories. And if the thought of becoming "efficient" at generating body fat doesn't make you want to drop the jelly beans, you must be crazy.

And It Gets Worse...

The high-sugar rats didn't just get fat and look bad in their bikinis, they also showed signs of liver damage. "The liver accumulating more fat mimics the effect of non-alcoholic fatty liver disease," said Czaja. Low-fat, high-sugar diets also appear to increase the bad gut bacteria associated with liver damage.

Not bad enough? The sugary diets even induced chronic inflammation in the intestinal tract and brain. When your brain gets inflamed it damages the vagus nerve, altering gut-brain communication. That affects your ability to feel full, leading of course to overeating.

Take-Home Lessons

Fat-free junk food is still junk food. Duh. And very low fat diets should have died in the 90's along with the Spice Girls.

We could summarize here by saying "eat a balanced diet" but it goes deeper than that. For overall health, performance, and good body composition, eat protein, carbs, and fats, BUT make sure those are quality proteins, quality carbs, and quality fats.

Chris Shugart is T Nation's Chief Content Officer and the creator of the Velocity Diet. As part of his investigative journalism for T Nation, Chris was featured on HBO’s "Real Sports with Bryant Gumble."